Mask forming



Jan. l0, 1967 J. P. FIORE 3,296,850

MASK FORMING Filed Aug. 25, 1964 5 Sheets-Sheet l rllllllllll"` r n 15aE //U liz n vla-S lawy n Jan. 10, 1967 J. P. FIORE l 3,296,850

`MASK Pom/[ING Filed Aug. 25, 1964 sneetsfsheet 2 PRIOR ART AND FlG.4

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5 Sheets-Sheet 3 'lll J. P. FIORE MASK FORMING Il 12d INVENTOR. Joseph@Fabre BY W Jan. 1o, 1967 Filed Aug. 25, 1964 llm United States PatentO" 3,296,850 MASK FURMING Joseph P. Fiore, Wheeling, Ill., assigner toThe Rauland Corporation, Chicago, Ill., a corporation of Iilmois FiledAug. 25, 1964, Ser. No. 391,986 6 Claims. (Cl. 72-351) This invention isdirected to the manufacture of a shadow-mask type of color televisiontube and is especially concerned with the formation of the shadow-maskor color selection barrier of such a tube.

In one commercial form of the shadow-mask color tube, the screen isformed directly on the faceplate and comprises a multiplicity of triadsor three-element phosphor clusters disposed `over the entire screenarea. The three phosphor elements of any such triad respond when scannedby a |beam of electrons and emit light of the three primary colors, red,green and blue. Usually, the tube has three electron guns each of whichdirects a beam of electrons toward the screen and these beams arecontrolled by a common deiiection eld to scan the screen simultaneously.The various color fields of an image result from imposing on the beam ofeach gun chroma information pertaining to the color field assigned tothat gun and by confining the beam issuing from any such gun to thephosphor dots that emit light of that particular color.

The restriction of each gun to its assigned phosphor dots, or what issometimes referred to as color selection, is accomplished by a parallaxbarrier in the form of an apertured mask interposed between the familyof guns and the screen. The mask has a multiplicity of apertures and thephysical structure is arranged to the end that any gun sees only itsassigned phosphor elements through the mask apertures. It is preferredthat the apertures of the mask to be `arranged in a field which has thesame configuration as the screen of the tube, that is to say, theapertures are arranged in a circular field or array for `a round tubeand are arranged in a rectangular field for a rectangular tube.

It is also important for optimum operation to control the spacing of themask from the screen. From the standpoint of the parallax principlesconsidered alone, and this, of course, is the basis of attainingeffective color selection, there is a uniform spacing of mask to screenacross the scan raster. If the screen is on the faceplate, which usuallyis a sector of a sphere, then it is appropriate that the shadow-masklikewise be a spherical section. This is the structure currently in usealthough it is also known that the screen and parallax barriers may beplanar or they may be cylindrical in configuration.

It will be appreciated that the formation of an aperture pattern in themask is a difiicult problem, bearing in mind the need for controllingthe size and disposition of the apertures throughout the mask area.Techniques have been developed by which the mask is formed throughetching of the mask material which is usually steel. After the apertureshave been formed in the mask and the blank has been suitably annealed,it is formed to the desired configuration. It has been the practice tomount the mask blank in a press in which cooperating die elements clampthe blank at the edge of the aperture field and, while it is thusclamped, shaping is accomplished by drape drawing over a suitably formedpunch.

Although this permits shaping the mask to the desired configuration, itsuffers from the disadvantage of introducing a non uniform elongation tothe apertures in the mask, especially those at the edge of the field.This results from the fact that the mask is clamped and held fixed atthe periphery of the aperture field and since the peripheral aperturesare held against movement, they 3,296,850 Patented Jan. 10, 1967 lCCsuffer less elongation in the drawing process. As a consequence, thecenter to center spacing of the apertures is not uniform throughout thefield.

Accordingly, it is an object of the invention to provide an improvedmethod for forming the shadow-mask of a shadow-mask type of colortelevision tube.

It is another object of the invention to provide a method for formingthe shadow-mask of such a turbe in which uniform center-to-centerspacing of the mask apertures is maintained.

It is a specific object of the invention to provide 4an improved methodfor forming the shadow mask for such a tube characterized by the factthat the center to center spacing of the apertures is controllable.

Another particular object of the invention is to provide an improvedmethod for forming a shadow mask without introducing non-uniformitiesinto the aperture field of the mask.

In accordance with the method of the invention the mask of a shadow-masktype of color cathode ray tube is formed from a sheet of metal having amultiplicity of apertures within a field of predetermined configurationbounded by a strip of the metal. The method of the inventionaccomplishes forming of the mask without introducing non-uniformities,especially variations in the center to center spacing of the maskapertures throughout the aperture field. The method comprises clampingthe sheet along a ciamping line within the boundary strip of the sheetbut spaced a predetermined minimal distance from the aperture field. Theclamped sheet is then drawn over a punch to drape draw the Sheet to thecontour of the punch and to draw a fillet in the sheet. The punch hasthe same peripheral configuration as the aperture field and an arealarger than that of the field Ibut smaller than that enclosed by theclamping line to locate the fillet in the portion of the strip betweenthe field and the clamping line. Thereafter, the sheet is unclamped andthe remaining portion of the boundary strip beyond the clamping line isformed into a skirt extension of the fillet.

This method may be employed in forming the shadowmask for round orrectangular tubes or tubes of any other acceptable configuration.Moreover, it is useful in the manufacture of tube structures in whichthe mask to screen spacing is uniform or non-uniform since this iscontrollable through the contour of the draw die or punch.

The features of the present invention which are believed to be novel areset forth with particularity in the appended claims. The invention,together with further objects and advantages thereof, may best beunderstood by reference to the following description taken in connectionwith the accompanying drawings, in the several figures of which likereference numerals identify like elements, and in which:

FIGURE 1 is an elevational view, partly in section, of a press forpracticing the method of the invention;

FIGURE 2 is an enlarged View taken along line 2-2 of FIGURE l;

FIGURES 3-6, inclusive, are views representing various positions of theapparatus of FIGURE 1 in the mask forming process;

FIGURE 7 comprises curves used in explaining the method of theinvention;

FIGURES 8 and 9 are used to explain the application of the inventivemethod in forming a rectangular mask.

Referring now more particularly to FIGURE 1, the apparatus thererepresented is a die press for carrying out the method of the inventionin forming the mask of a circular shadow-mask type of color televisiontube. The press, as a structure, is conventional, having a verticalframework 10 which supports the punch and die components as well as anhydraulic system for exerting the necessary drawing forces or pressures.The punch over which a mask blank is to be drape drawn is designated 11.It is mechanically supported from, and centrally located of, a fixed beda of the press frame structure. If it be assumed that the mask is tohave the shape of a spherical section, punch 11 will have the same shapeand will have a radius corresponding to that to which the mask blank isto be drawn.

There is a pressure ring assembly concentrically positioned with respectto punch 11. This assembly includes a base member 12 having a number ofbushings 12a which receive vertically extending guide posts 10b of theframe structure of the press; it is convenient to have four suchbushing-guide arrangements located at the corners of the pressure ringassembly which has a generally rectangular overall configuration. Thebase 12 has another series of apertures 12b arranged on a circle betweenthe inner periphery of the base and its bushing provisions 12a. Thisseries of apertures 12b threadably receives coupling members 13a whichextend vertically of a platen 13 and mechanically couples the pressurering assembly to this platen in order that they may move unitarily,being guided by posts 10b. There is an upper or die portion 12c of thepressure ring removably secured to base 12. The inner diameter of thepunch ring is only slightly larger than the external diameter of punch11. There are a number of locating pins 12a' accommodated by aperturesin die ring 12e. Generally, there are three such loeating elementsspaced from one another on die 12C and spring pressed normally toproject above the upper surface of the die but arranged to recede intodie recesses which accommodate the bias springs of the locating pins.

Disposed above pressure ring 12 is a draw ring 14 which, likewise, hasbushings 14a through which guide posts 10b extend. The draw ring hassimilar dimensions to the die portion 12C of the pressure ring and theirfacing surfaces are lapped to represent mating die areas. The internaldiameter of draw ring 14 is slightly greater than the internal diameterof pressure ring 12. It is dimensioned to have an internal diameterexceeding the external diameter `of the piston or cylindrical portion ofpunch 11 by approximately twice the thickness of the mask blank.Disposed within draw ring 14 is a resilient pressure pad 15 supportedfrom the draw ring by means of pins 15a surrounded by springs which tendto extend the pad in the direction of pressure ring 12. The entireassembly of draw ring and pad is mechanically secured to the piston 16of an hydraulic motor 17 constructed in the upper portion of the frame10 of the press. The hydraulic system is designated schematically at 18.It is of conventional construction and is employed to advance the piston16 downwardly on a pressure stroke during the drawing operation and toretract it after that operation has been completed.

Similarly, there is an hydraulic system comprising a piston 19 and motor20 formed in the bed of the press and having a similar hydraulic system21 through which piston 19 may be moved to vary the position of platen13 and pressure pad 12 to accomplish mask forming. The verticaldisplacement of pistons 16 and 19 is, of course, controlled by thehydraulic systems. No claim of invention is predicated on this portionof the die press which may be of well-known design, programmed throughmicroswitches or the like to achieve precisely controlled displacementof the die parts in the drawing operation.

The mask blank to be formed for a circular tube has a multiplicity ofapertures within a field of predetermined configuration, specifically,within a circular field. This field is bounded by a strip of the blankmetal. A segment of such a shadow-mask blank is shown in FIGURE 2 wherethe center to center spacing of the apertures is designated by thedimension line S and the boundary strip of metal S' is the material ofthe blank extending from the periphery of the circular field ofapertures to the outer periphery of the mask. Usually, the mask blank isannealed steel. As indicated in FIGURE 2, there is a notch N formed atthe outer edge of boundary strip S to accept a locating pin 12d. Asthere are three such pins, there are a similar series of three notches.The pin and notch locations may be arranged to the end that the blankwill fit pressure ring 12C in only a single position which facilitatesdesignating a top or bottom portion for the mask. In practicing theinvention, the circular mask blank is first positioned on draw ring 12Cby means of the locating pins 12d and the notches N. The draw ring isthen in the position illustrated in FIGURE l. The initial or startingposition is one in which platen 13 has been advanced to its uppermostposition by piston 19.

After the blank has been positioned, hydraulic fluid is admitted tocylinder 17 and draw ring 14 closes down upon pressure ring 12. Thepositions that the die sections assume is that of FIGURE 3 from which itis seen that locating pins 12d recede into the apertures provided inpressure ring 12C. At this step, the mask blank is clamped along aclamping line L located within strip S of the blank and spaced apredetermined minimal distance AS from the periphery of the aperturefield. The distance AS is large compared to the diameter of the maskapertures and preferably is at least equal to several times the diameterof the mask apertures.

While pressure exerted concurrently on the draw and pressure ringsprovides the necessary clamping force for the blank, the pressureexerted on the draw ring is the greater and the differential pressurecauses the closed die assembly to descend, drawing the mask blank overpunch 11 to drape draw the sheet to the contour of the punch. Therelative positions of the dies and the punch is that of FIGURE 4.

The descending stroke of the punch assembly is continued beyond that ofFIGURE 4 to achieve the position illus-trated in FIGURE 5 in order todraw a fillet F in the mask sheet or blank. While the peripheralconfiguration of punch 11 is the same as that of the field of apertures,both being circular for the case under consideration, the area of thepunch is larger than that of the aperture field but smaller than thearea enclosed by clamping line L. As a consequence, the fillet F islocated in the portion of strip S between the aperture field andclamping line L.

The final position of the cooperating dies in relation to punch 11 hasan important bearing on the characteristics of the formed mask. This isbest illustrated by the curves of FIGURE 7 in which the broken-linecurve C1 depicts the variation of the dimension S, the center to centerspacing of the apertures, in terms of distance from the center of themask blank if the draw and pressure rings stop in the position of FIGURE4 without having first pulled the radius or drawn the fillet F in thesheet. The curve indicates a non-uniform center to center spacing whichis undesirable. By continuing the draw 'to attain the position of FIGURE5, the center to center separation of the mask apertures may be madesubstantially uniform as represented by full line curve C2. Intermediatefinal positions in the drawing operation permit controlling the aperturespacing but it is generally preferred that the spacing be uniform overthe aperture field of the mask. This is attained by drawing the filletto the point which is essentially tangent to the radius 11a of thepunch.

After the fillet has been drawn to the appropriate depth, theprogramming of the die press retracts piston 19 to lower platen 13 andpressure ring 12 as indicated in FIG- URE 6. This unclamps the sheet byseparating the draw and pressure rings. The descent of draw ring 14 isnow continued to form the portion of strip S which extends from clampingline L radially outwardly into a skirt extension of fillet F whichcompletes the mask formation.

In the final descent of draw ring 14, pressure pad 15 is brought to bearagainst the aperture field of the formed mask blank as indicated inFIGURE 5. As the draw ring is returned to the starting position ofFIGURE 1,

pressure pad 15 retains the formed blank on punch 11 and releases itspressure thereon after draw ring 14 has cleared away from the blank.Finally, however, the pressure pad 15 rises with draw ring 14 andreleases the blank. In the last step of the process pressure ring 12 iselevated to its starting position of FIGURE 1 which strips the formedblank free of punch 11 so that the operator may remove it from thepress.

In forming the mask blank for a 2l inch circular tube, the hole diameteris appropriately l0 to l2 mils and the separation of clamping line Lfrom the edge of the aperture field is approximately V16 of an inch. Itis found that by drawing the blank over the punch, forming the fillet F,the desired uniform elongation of apertures particularly at the marginalportions of the field is attained and a substantially uniform center tocenter spacing of apertures is retained over the field.

Essentially, the same method is employed in forming the mask for arectangular tube. In this case, the plan view of the punch and pressurering is that of FIGURE 9. If it again be assumed that the mask is tohave the configuration of a spherical section, the dimension of thepunch from the center to various points on its periphery is non-uniform.For example, the radius R1 to the corner is a maximum dimension Whereasthe radius R2 to the middle of the long dimension of the rectangle isthe shortest. Therefore, the specific shape of the draw ring 14 ofFIGURE 8 and its pressure ring 12, employed for forming the rectangularmask, is specifically different from the corresponding die sections ofthe arrangement of FIG- URE l. In FIGURE 1, the mating die surfaces aresimple planar surfaces whereas the view of FIGURE 8 shows that for therectangular mask, the die elements have a spherical contour. This, ofcourse, results from the fact that the punch in the latter case has aperipheral configuration of a rectangle whereas in the former case ithad the symmetrical configuration of a circle. Preferably, for formingrectangular masks the spheroidal surfaces of the mating dies have thesame radius of curvature as the contiguous periphery of punch 11.

The apparatus of FIGURES 8 and 9 carries out essentially the sameprocess as described in the discussion 0f FIGURES 3 to 7 but in thiscase bringing the draw ring 14' against pressure ring 12 results inpreforming. The sheet or mask blank is a flat planar sheet at the outsetand clamping it between dies 12 and 14 which have a spherical contourcauses the sheet to have a similar contour. This is referred to aspreforrning. A color tube including a rectangular mask which may beformed through the described apparatus is described and claimed inPatent 2,897,392, issued July 28, 1959, in the name of Joseph P. Fioreand assigned to the assignee of the present invention.

The description has proceded on the assumption that punch 11 is asection of a sphere as would be used in drawing a mask blank that is tobe spherical in configuration. Obviously, the invention is not confinedto the use of perfect spherical sections; the punch may havespecifically different contours to which the mask blank may be formed bydrape drawing. For example, it is sometimes advantageous to have asmaller mask to screen spacing at the edges than at the center of themask. To achieve this result punch 11 has a larger radius at itsperiphery than at the center and dimensional change is Smooth andcontinuous rather than sharp and discontinuous.

While particular embodiments of the invention have been shown anddescribed, it will be obvious to those skilled in lthe art that changesand modifications may be made without departing from the invention inits broader aspects, and, therefore, the aim in the appended claims isto cover all such changes and modifications as fall within lthe truespirit and scope of the invention.

I claim:

1. In the manufacture of a shadow-mask type of color cathode-ray tube,the method of forming a shadow-mask from a sheet of metal having amultiplicity of apertures 6 within a field of predeterminedconfiguration bounded by a strip of said metal and without introducingnon-uniformities into said field, which method comprises:

clamping said sheet along a clamping line within said strip and spaced apredetermined minimal distance from said field; drawing said sheet overa punch to drape draw said sheet to the contour of said punch and todraw a fillet in said sheet, said punch having the same peripheralconfiguration as said field and an area larger than said field butsmaller than that enclosed by said clamping line to locate said filletin the portion of said strip between said field and said clamping line;

unclamping said sheet and forming the remaining portion of said stripbeyond said clamping line into a skirt extension of said fillet.

2. In the manufacture of a shadow-mask type of color cathode-ray tube,the method of forming a shadow-mask from a sheet of metal having amultiplicity of apertures within a field of predetermined configurationbounded by a strip of said metal and Without introducingnon-uniformities into said field, which method comprises:

clamping said sheet along a clamping line located within said strip andspaced from said field by an amount that is large compared to thediameter -of said apertures;

drawing said sheet over a punch to drape draw said sheet to the contourof said punch and to draw a fillet in said sheet, said punch having thesame peripheral configuration as, but a larger area than, said field tolocate said fillet in the portion of said strip between said field andsaid clamping line;

unclamping said sheet and forming the remaining portion of said stripbeyond said clamping line into a skirt extension of said llet.

3. In the manufacture of a shadow-mask type of color cathode-ray tube,the method of forming a shadow-mask from a sheet of metal having amultiplicity of apertures within a eld of predetermined configurationbounded by a strip of said metal and without introducingnon-uniformities into said field, which method comprises:

clamping said sheet along a clamping line located within said strip andspaced from said field by an amount that is large compared to thediameter of said apertures;

drawing said sheet over a punch to drape draw said sheet to the contourof said punch and to draw a fillet in said sheet of such depth that thecenter-to-center spacing of the apertures is substantially uniformwithin said field, said punch having the same peripheral configurationas, but a larger area than, said field to locate said fillet in theportion of said strip Ibetween said field and said clamping line;

unclamping said sheet and forming the remaining portion of said stripbeyond said clamping line into a skirt extension of said fillet.

4. In the manufacture of a shadow-mask type of color cathode-ray tube,the method of forming a shadow-mask from a sheet of metal having amultiplicity of apertures within a circular field bounded by a strip ofsaid metal and without introducing non-uniformities into said field,which method comprises:

clamping said sheet along a circular clamping line located within saidstrip and spaced from said field by an amount that is large compared tothe diameter of said apertures;

drawing said sheet over a punch to drape draw said sheet to the contourof said punch and to draw a fillet in said sheet, said punch being asubstantially spheroidal section having a chord dimension larger thanthe diameter of said field to locate said fillet in the portion of saidstrip between said field and said clamping line;

unclamping said sheet and forming the remaining portion of said stripbeyond said clamping line into a skirt extension of said fillet.

5. In the manufacture of a shadow-mask type of color cathode-ray tube,the method of forming a shadow-mask from a sheet of metal having amultiplicity of apertures within a rectangular eld bounded by a strip ofsaid metal and without introducing non-uniformities into said field,which method comprises:

clamping said sheet along a rectangular clamping line located withinsaid strip and spaced from said field by an amount that is largecompared to the diameter of said apertures; drawing said sheet over apunch to drape draw said sheet to the contour of said punch and to drawa fillet in said sheet, said punch being a substantially spheroidalsection, having a projected area of rectangular configuration and havingprincipal dimensions larger than the corresponding dimensions of saidfield to locate said fillet in the portion of said strip between Saidfield and said clamping line;

unclamping said sheet and forming the remaining portion of said stripbeyond said clamping line into a skirt extension of said fillet.

6. In the manufacture of a shadow-mask type of color cathode-ray tube,the method of forming a shadow-mask from a sheet of metal having amultiplicity of apertures within a rectangular field bounded by a stripof said metal and without introducing non-uniformities into said field,which method comprises:

preforming by clamping said sheet between a pair of mating dies havingspherically shaped die surfaces dimensioned to engage said sheet along arectangular clamping line located within said strip and spaced from saidfield by an amount that is large compared to the diameter of saidapertures;

drawing said sheet over a punch to drape draw said sheet to the contourof said punch and to draw a fillet in said sheet, said punch being asubstantially spheroidal section having a radius at the peripheryapproximately equal to radius of said die surfaces, having a projectedarea of rectangular configuration and having principal dimensions largerthan the corresponding dimensions of said field to locate said fillet inthe portion of said strip between said eld and said clamping line;

unclamping said sheet;

and forming the remaining portion of said strip beyond said clampingline into a skirt extension of said fillet.

References Cited by the Examiner UNITED STATES PATENTS 689,330 3/1901Thurber 72-350 1,513,644 10/ 1924 Sindelar 72-328 FOREIGN PATENTS637,759 5/1950 Great Britain.

CHARLES W. LANHAM, Primary Examiner.

RICHARD J. HERBST, Examiner.

1. IN THE MANUFACTURE OF A SHADOW-MASK TYPE OF COLOR CATHODE-RAY TUBE,THE METHOD OF FORMING A SHADOW-MASK FROM A SHEET OF METAL HAVING AMULTIPLICITY OF APERTURES WITHIN A FIELD OF PREDETERMINED CONFIGURATIONBOUNDED BY A STRIP OF SAID METAL AND WITHOUT INTRODUCINGNON-UNIFORMITIES INTO SAID FIELD, WHICH METHOD COMPRISES: CLAMPING SAIDSHEET ALONG A CLAMPING LINE WITHIN SAID STRIP AND SPACED A PREDETERMINEDMINIMAL DISTANCE FROM SAID FIELD; DRAWING SAID SHEET OVER A PUNCH TODRAPE DRAW SAID SHEET TO THE CONTOUR OF SAID PUNCH AND TO DRAW A FILLETIN SAID SHEET, SAID PUNCH HAVING THE SAME PERIPHERAL CONFIGURATION ASSAID FIELD AND AN AREA LARGER THAN SAID FIELD BUT SMALLER THAN THATENCLOSED BY SAID CLAMPING LINE TO LOCATE SAID FILLET IN THE PORTION OFSAID STRIP BETWEEN SAID FIELD AND SAID CLAMPING LINE; UNCLAMPING SAIDSHEET AND FORMING THE REMAINING PORTION OF SAID STRIP BEYOND SAIDCLAMPING LINE INTO A SKIRT EXTENSION OF SAID FILLET.